Therapeutic coatings may be added to implantable medical devices such as stents. Therapeutic coatings may provide benefits relative to a disease condition, in particular in reducing endothelial restenosis and in reducing thrombus at the stent/body lumen interface.
The bioactive substance may be dissolved or dispersed into a suitable liquid polymer/solvent solution, which may then be deposited onto the device's metal substrate using one of a number of different coating processes.
Some coating processes include air-jet spray, electrostatic discharge deposition, dip coating, fluidized bed, bubble jet printer, and roll coating. An exemplary embodiment of the present invention may provide a deposition process that mitigates the high costs of some drug-eluting substances by applying the coating in a cost-efficient way. A coating process with the ability to deposit two different drug-eluting substances, one on the inside of the stent and one on the outside, may be advantageous.
Drug-eluting stents may be used to address issues of endothelial restenosis and thrombus, which may form at the stent/body lumen interface. These two different responses to the stent may also be further separated into an external and internal orientation relative to the stent. Endothelial restenosis may be a response of the cell tissue to the outside contacting surface of the outside of the stent and may include unwanted cell growth. Thrombus may be a response to the stent cell edges and the internal surface of the stent and may include a clotting of red blood cells.
An anti-restenotic coating may be deposited over the complete surface of the stent, including the inside surface, where it may not be required or may be of less benefit. The main reason for coating the entire surface of the stent may be to ensure, in the absence of a strong intermolecular bond between the coating and stent, that the stent is encapsulated with coating material. An encapsulated coating may help retain the coating on the stent. Polymer-based coatings may not adhere to stents constructed of stainless steel, nitinol, and/or other materials, and the most effective manner of coating a stent may be to completely encapsulate the stent. In this manner, the polymer coating bonds to itself to maintain the integrity of the coating.
Conventional mounts for individual stents may include a crosswire, which may in turn be mounted on a supporting wire preform which may be referred to as a C frame. A vertical rotary spindle may carry in the upward facing end a mating drive socket into which the lower end of the C frame is received and engaged. When the nozzle is spraying coating fluid, the C frame and stent drive arrangement may be rotated and raised to bring the stent into the path of the spray plume. The rotary drive and mount may also be designed to pass in a linear manner through the plume from one side to the other. This may ensure a full and/or equal coverage of the stent, and may also ensure that the inside surface of the stent is also coated.
There thus is a need for a method of providing a differential coating on a medical appliance, and in particular a method for depositing a different coat on the inside of a stent than the coat deposited on the outside of the stent.